105 lines
3.1 KiB
Java
105 lines
3.1 KiB
Java
/*
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* Copyright (C) 2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.hardware.camera2.utils;
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import android.compat.annotation.UnsupportedAppUsage;
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import android.os.Build;
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/**
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* Provide hashing functions using the Modified Bernstein hash
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*/
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public final class HashCodeHelpers {
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/**
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* Hash every element uniformly using the Modified Bernstein hash.
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*
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* <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
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*
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* @param array a non-{@code null} array of integers
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*
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* @return the numeric hash code
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*/
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@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
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public static int hashCode(int... array) {
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if (array == null) {
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return 0;
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}
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/*
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* Note that we use 31 here instead of 33 since it's preferred in Effective Java
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* and used elsewhere in the runtime (e.g. Arrays#hashCode)
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*
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* That being said 33 and 31 are nearly identical in terms of their usefulness
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* according to http://svn.apache.org/repos/asf/apr/apr/trunk/tables/apr_hash.c
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*/
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int h = 1;
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for (int x : array) {
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// Strength reduction; in case the compiler has illusions about divisions being faster
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h = ((h << 5) - h) ^ x; // (h * 31) XOR x
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}
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return h;
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}
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/**
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* Hash every element uniformly using the Modified Bernstein hash.
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*
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* <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
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*
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* @param array a non-{@code null} array of floats
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*
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* @return the numeric hash code
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*/
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public static int hashCode(float... array) {
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if (array == null) {
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return 0;
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}
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int h = 1;
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for (float f : array) {
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int x = Float.floatToIntBits(f);
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h = ((h << 5) - h) ^ x; // (h * 31) XOR x
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}
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return h;
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}
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/**
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* Hash every element uniformly using the Modified Bernstein hash.
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*
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* <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
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*
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* @param array a non-{@code null} array of objects
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*
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* @return the numeric hash code
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*/
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public static <T> int hashCodeGeneric(T... array) {
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if (array == null) {
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return 0;
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}
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int h = 1;
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for (T o : array) {
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int x = (o == null) ? 0 : o.hashCode();
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h = ((h << 5) - h) ^ x; // (h * 31) XOR x
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}
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return h;
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}
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}
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